Study On The Damage Mechanism Of Multilayer Composites Under Highenergy Laser Irradiation

Composite materials have become the main structural materials for aerospace weapons and equipment due to their high specific strength and modulus,corrosion resistance,and designable performance.Multilayer composite materials have been widely used in supersonic vehicles due to their excellent heat-proof/load-bearing integrated performance.Lasers have been extensively and deeply studied in the field of advanced weapons and equipment because of their good unidirectionality,rapid response,and high accuracy.The emergence of laser weapons makes the aircraft face the danger of ablation damage caused by high-energy laser weapons during the service period,which puts forward new requirements for the laser ablation resistance of composite structures.Laser ablation of composite materials is accompanied by a series of complex physical and chemical changes,and its ablation damage mechanism is complex,which brings great challenges to the evaluation and simulation analysis of laser damage.This paper takes glass fiber/phenolic composite material and carbon fiber/bismaleamide composite material as the research objects,and performs laser damage tests on three samples of glass fiber/phenolic composite material flat plate,multi-layer composite material flat plate and composite sandwich structure.The ablation laws of these three structures under different laser parameters and the mechanical properties after laser ablation are systematically studied.It reveals the damage behavior and failure mechanism of high-power laser to multilayer composite materials,and provides theoretical support,data foundation and experimental basis for the research and development of high-energy laser weapons and aircraft anti-laser reinforcement technology.The main research results are as follows:(1)The glass fiber/phenolic composite material was prepared by the compression molding process,and the laser damage test was performed on the glass fiber/phenolic composite material.The ablation mechanism of glass fiber/phenolic composite material under intense laser irradiation and the influence of laser parameters on its ablation efficiency were studied.The results show that both the diameter of the ablation pit and the diameter of the transition zone are positively correlated with the total irradiated energy,and the power density has a significant influence on the diameter of the ablation pit;the breakdown time of the target material is approximately inversely proportional to the power density,while the breakdown time decreases linearly as the irradiated area increases.During the laser ablation process,the resin layer is the first to be pyrolyzed,generating carbon residues to form a residual carbon skeleton,which prevents further laser ablation.At the same time,a large amount of pyrolysis gas generated by pyrolysis prevents the entry of oxygen,which results in that only when the temperature reaches the vaporization temperature of the residual carbon,the laser can continue to ablate downward.However,since the vaporization temperature of the molten glass fiber is much lower than the vaporization temperature of the residual carbon,the glass fiber is the first to vaporize and disappear,forming a vertical and horizontally stacked carbon skeleton porous structure.(2)Based on the theory of one-dimensional heat conduction,a mathematical model for laser ablation of glass fiber/phenolic composite materials is established,and the laser ablation process is simplified to the transient heat conduction problem of a semi-infinite plate.The relationship between laser ablation speed and laser parameters is obtained,which provides a theoretical basis for the ablation law of glass fiber/phenolic resin composites.Based on the conservation of energy,a macro-micro dual-scale analysis model was established to simulate the laser ablation process.The temperature distribution and temperature change history during the laser ablation process are obtained,and the temperature calculation results are compared with the backplane temperature tested by the laser ablation test.The results are in good agreement and the accuracy of the analysis model is verified.(3)Starting from the integrated design of heat protection/load bearing,a double-layer composite structure was prepared by the co-bonding method,and a strong laser damage test was performed on it,and the bending performance before and after the damage was studied.The results show that laser irradiation changes the failure mode of multilayer composite materials,which is due to the existence of interface thermal resistance hindering the transfer of laser energy.Energy accumulates in the interface layer,and the melting of the resin causes the strength of the bonding interface to decrease,and it is the first to crack under the action of bending load.Laser irradiation seriously reduces the bending strength of the structure.Under lower power density irradiation,the laser cannot effectively damage the carbon fiber composite material.The ablated multilayer board still has good strong rigidity.However,under higher power and longer time,the carbon fiber composite material is severely ablated,and the strong rigidity of the structure drops sharply at this time.(4)The bending and lateral pressure properties of the composite sandwich structure before and after laser ablation were studied.The test found that the mechanical properties of the composite sandwich structure after being damaged by different laser irradiation methods are quite different,and the damage to the core and the panel joint has the most serious impact on the mechanical properties.Under the action of bending load,the failure mode before and after laser irradiation is basically the same,both of which are separation of face and core and fracture of core.The ablation damage of the panel and the joints caused by laser irradiation destroys the overall stability of the structure,resulting in a large difference in the form of damage before and after ablation of the sandwich structure under the action of compressive load.